Sunscreen Formulation Analysis and OMC Stability

Thank you for your detailed questions and sharing your formulas. It shows you have done thorough research, which is excellent for formulation!

Let's address the stability of OMC and then review your sunscreen formulas.

Is OMC Unstable?

Based on the information and research shared, OMC (Octyl Methoxycinnamate) is a widely used and effective UVB filter. While it does undergo some photodegradation when exposed to UV light, meaning its structure changes over time (partially converting to Z-OMC), it is generally considered sufficiently stable for typical daily use. It doesn't become completely ineffective immediately. Antioxidants like Vitamin E can be added at a low percentage (around 0.1%) to help improve its stability.

It's important to remember that all sunscreen filters, whether chemical or physical, can be affected by UV exposure over time. The key is the overall formulation's ability to provide protection for the intended duration of use.

Review of Your Sunscreen Formulas

Here is an analysis of your three proposed formulas:

Formula 1: Physical Sunscreen

• Ingredients: Zinc Oxide 15%, Titanium Dioxide 7%, LipidSoft Lite 30%, Water, Light Cream Maker 1%, Preservative.
• Evaluation: This formula uses physical filters, Zinc Oxide and Titanium Dioxide, which provide broad-spectrum UVA/UVB protection and are known for their good photostability. Your mixing method of dispersing the powders in the oil phase (LipidSoft Lite) before emulsifying with Light Cream Maker and water is a standard and effective approach for physical sunscreens.
• Stability: This formula is expected to be stable and provide reliable sun protection.

Formula 2: Hybrid Sunscreen

• Ingredients: Zinc Oxide 10%, DHHB 5%, OMC 10%, LipidSoft Lite 30%, Water, Light Cream Maker 1%, Preservative.
• Evaluation: This is a well-designed hybrid formula combining the broad-spectrum protection of Zinc Oxide with the strong UVA protection of DHHB and UVB protection of OMC. This combination provides excellent broad-spectrum coverage.
• OMC vs. Octocrylene: OMC is a suitable choice for UVB protection in this formula. Octocrylene is another option, often used to stabilize Avobenzone (which is not in this formula). While Octocrylene might be slightly cheaper, OMC is a very effective filter. The choice depends on specific formulation goals and desired performance characteristics. Given the filters present, OMC works well here.
• Mixing Method: Dissolving DHHB and OMC in LipidSoft Lite, then adding Zinc Oxide and emulsifying with Light Cream Maker and water is a logical method.
• Stability: This formula is expected to have good stability for normal daily sun exposure.

Formula 3: Chemical Sunscreen

• Ingredients: Oxybenzone 10%, DHHB 10%, OMC 10%, LipidSoft Lite 30%, Water, Light Cream Maker 1%, Preservative.
• Evaluation: This formula uses a combination of chemical filters for broad-spectrum protection. Oxybenzone provides UVA/UVB coverage, DHHB is a strong UVA filter, and OMC is a strong UVB filter. This blend offers comprehensive protection.
• Stability for Brief Exposure: For short, intermittent sun exposure (like walking between buildings), this formula should provide sufficient stability and protection.
• Alternative Strategy (Avobenzone): As discussed, a common alternative strategy for strong UVA protection is to use Avobenzone (a highly effective UVA filter) stabilized by filters like Oxybenzone, Octocrylene, or Octisalate, because Avobenzone is incompatible with OMC and physical filters like Zinc Oxide and Titanium Dioxide. Your formula uses OMC and Oxybenzone without Avobenzone, which is a valid approach, but if maximum UVA coverage from chemical filters was the sole goal, an Avobenzone-based system with stabilizers would be another path.

Adding Vitamin E and Q10 & Modified Chemical Formula

You asked about adding Vitamin E and Q10 for antioxidant benefits and proposed a modified chemical formula with high percentages of UV filters and emollients.

• Antioxidants (Vitamin E, Q10): While Vitamin E and Coenzyme Q10 are excellent antioxidants that can help protect skin from free radical damage caused by UV exposure, incorporating significant amounts into a lightweight sunscreen formula can be challenging. These are oil-soluble ingredients, and adding them increases the oil phase percentage. This can make the sunscreen feel heavy or greasy and potentially destabilize the emulsion, especially with emulsifiers designed for lighter textures like Light Cream Maker (which has a limit on the oil phase it can handle, typically up to 20%). If you want antioxidant benefits, it's often more effective to use them in separate skincare products (like a serum or night cream) or include only a very low percentage (e.g., 0.1% Vitamin E) in the sunscreen primarily for its role in stabilizing the UV filters, rather than for direct skin antioxidant benefits.
• Modified Chemical Formula Proposal: Your proposed formula with high percentages of SPF Protect Ultra II (20%), Lipidsoft lite (10%), DHHB (10%), Oxybenzone (10%), and Vitamin E (1%) results in a very high total oil/filter percentage (over 50%). This high load will almost certainly lead to a heavy, sticky texture and is likely beyond the capacity of Light Cream Maker to properly emulsify and stabilize, increasing the risk of formula separation.
• Recommended Adjustment: To achieve high protection (like PA++++ and SPF 50+) while maintaining a more acceptable texture and stability, it is recommended to use lower percentages of the UV filters and oil-soluble ingredients. For example, using DHHB at around 7%, SPF Protect Ultra II at around 15%, Oxybenzone at around 5%, and Vitamin E at 0.1% is a more balanced approach that can still provide excellent protection without making the formula too heavy or unstable.

Your initial formulas are good starting points, and understanding the properties and compatibilities of the different UV filters and formulation ingredients is key to successful sunscreen development. Always consider the balance between protection level, texture, stability, and cost.